366 



NA TURE 



[August 20, 1908 



OUR BOOK SHELF. 



The Saniiation of Recreation Camps and Parks. By 

 Dr. Harvey B. Bashore. Pp. xii+iog. (New 

 York : John Wiley and Sons ; London : Chapman 

 and Hall, Ltd., 1908.) Price 4s. 6d. net. 

 This small work may be read with interest and profit 

 by those who camp out, and also by those who, for 

 motives of sport, itc, roam about country districts. 

 The sanitation of military and labour camps is not dealt 

 with, but the author occasionally makes military 

 experiences his te.xt for the need of the sanitary pre- 

 cautions which he impresses. The sanitary rules 

 advocated for camps embrace the careful screening- of 

 food from flies and dust until it is consumed; the 

 avoidance of all brook or creek waters for drinking- 

 purposes, unless a careful survey has been made of 

 the source of the brook or creek, and this has dis- 

 closed no access of harmful pollution ; the daily burn- 

 ing or burying of all waste, solid and liquid ; the 

 desirabilitv of carefully selecting a special area for the 

 disposal of fteces, the exclusive use of this particular 

 area, and the prompt covering of all dejecta by 

 "mother earth." In districts where mosquitoes are 

 troublesome and dangerous, adjacent brooks or jX)ols 

 should be treated with kerosene every ten days, and 

 weeds and grass kept short around the camp. 



The work is well illustrated, and by the avoidance 

 of technical terms and the presentation of the subject 

 in an interesting and pleasing style the writer has 

 provided a most readable and useful little work. One 

 of the occasional digressions to be noted makes refer- 

 ence to the very common practice in towns of exposing 

 food to view in public places, without any protection 

 whatever from the gross contamination involved in 

 street dust. Certainly the practice cannot be de- 

 fended ; from the hygienic standpoint it is dangerous ; 

 to the contemplation of the refined it is disgusting; 

 and from the commercial standpoint it is wasteful, 

 for it must lead to a far quicker deterioration of the 

 article than would take place if food were properly 

 protected by glass. 



The Eve, its Elementary Anatomy, Physiology, and 

 Optical Constants. By Lionel Laurance. Pp. 100. 

 (London : The Orthos Press, 1908.) 

 This little book, according to its preface, has been 

 written for students in optics, and the author guaran- 

 tees the precision of the facts therein contained on 

 the ground that Mr. Lindsay Johnson has passed the 

 proofs. The anatomy of the, eye is fairly well de- 

 scribed, but we cannot say as much for the physiology. 

 On p. 21 we learn that " the visual purple, which is 

 quite sufficient to enable one to see in bright sun- 

 shine, is altogether inadequate to see in a dim light. 

 It is found that . . . none is found at the fovea. 

 The function therefore of the purple appears to be 

 to enable one to see better in a dim light." The 

 definition of the angle a is erroneous ; the angle 

 described is that termed P by precise ophthalmologists. 

 The estimation of distance is due very little to the 

 function of accommodation, but almost entirely to that 

 of convergence, as can very easily be proved. 



The subject of colour-blindness is indifferently well 

 described, as no mention is made of Dr. Edridge- 

 Green, although some of his- results have been given. 

 Students of optics will have niuch to complain of in 

 the last ten pages of the book on optical constants. 

 No proper use is made of algebraic signs ; thus the 

 anterior and posterior focal lengths of a refracting- 

 system are both expressed by the same sign, so that 

 they both apparently lie on the same side of the 

 system. .■Xgain, the focal length of the lens of the 

 eye is measured from its surface, a correction having 



NO. 2025, VOL. 78] 



been introduced for its thickness; yet in the calculation 

 on p. 90 the value assigned to F, should be the prin- 

 cipal focal distance measured from the corresponding 

 principal point. 



Before Adam. By Jack London. Pp. 30S. (London : 



T. Werner Laurie.) Price 6s. 

 In Mr. London's story a man has persistent dreams, 

 in which he sees "visions of myself roaming through 

 the forests of the younger world ; and yet it is not 

 myself that I see, but one that is only remotely a part 

 of me, as my father and my grandfather are parts of 

 me less remote. This other self of mine is an ancestor, 

 a progenitor of my progenitors in the early line of my 

 race, himself a progeny of a line that long before 

 his time developed fingers and toes and climbed up 

 into the trees. . . . An instinct is a racial memory 

 . . . there must be a medium whereby these memories 

 are transmitted from generation to generation. This 

 medium is what Weismann calls the germ-plasm. It 

 carries the memories of the whole evolution of the 

 race." 



Mr. London's theory of heredity is out of date. 

 Nevertheless his book is extraordinarily vivid and 

 convincing, and altogether delightful. Admirable as 

 fiction, it is also, b}' virtue of good psychology and 

 imaginative insight, in its way an inspiring work of 

 science. Reading it, one finds it hard not to believe 

 that our very distant ancestors lived just such a life 

 as Mr. London portrays — full of intense but transient 

 emotions, replete with danger and terror, but replete 

 also witli joys half human and half brute. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neittier can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



Bimetallic Mirrors made by Electro-deposition. 



Apropos of Mr. Cowper-Coles's exhibit at the recent 

 soiree of the Royal Society of metallic searchlight reflectors 

 made by the electro-deposition of copper upon a silver film 

 chemically deposited on glass, it may be interesting to 

 mention that some forty years .igo (I think in the year 

 1865) I spent a considerable time in experimenting in the 

 same direction. My object was to make a true " flat " for 

 the second reflection of a Newtonian telescope, with silver 

 surface as bright as that in contact with silvered glass and 

 without degradation from the true figure of the glass. The 

 last condition 1 was unable to fulfil. It had been rightly 

 judged that the outside surface of the silver film used by 

 M. Foucault could scarcely have the truth of figure or the 

 brilliancy of polish of the glass on which it had been de- 

 posited, hence the desirability of the object sought. 



However firmly and closely the silver film had adhered 

 to the glass, the moment the copper deposit commenced 

 upon it it became detached from the glass owing to the 

 contraction of the copper, and the surface which had been 

 plane became convex. 



This convexity seemed to be much the greatest in the 

 usual sulphate of copper solution, whh free acid, giving 

 a tough deposit. With one containing little or no free acid 

 and giving a crystalline deposit little contraction took 

 place and the face continued fairly fl.it, but. of course, the 

 process was tedious in the days of Daniell's cells, and I 

 doubt if I ever obtained a true enough surface for my 

 purpose. 



The problem, however, which Mr. Cowper-Coles has set 

 himself is a very different one. Extreme accuracy of 

 figure is relatively of smaller importance, and with the 1 

 devices of rotation of mirror and continual agitation of the | 

 solution, which, I believe, he has resorted to, and the latter ' ' 

 of which I found much improved the results, he may 



